Geo: Implement state machine on a state model (Refactoring)

What does this MR do and why?

We store verification status in a separate table but we define the state machine in the main model. This is confusing and it even led to a bug because the main model record has not to be touched when the status is updated. This MR moved state machine definition to a separate concern. This MR fixes the mentioned bug as a side-effect and it doesn't target it directly.

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